In installations for delivering liquid hydrocarbons, hydrocarbon delivery needs to be controlled in such a manner as to ensure that delivery is stopped when the hydrocarbon has too high a gas content. This applies particularly when air from various leaks in the circuits gets into the hydrocarbon. In prior art control systems, a valve device is used upstream from the hydrocarbon delivery tube for stopping the flow of hydrocarbon to the delivery end of the tube under certain circumstances. The valve is rated so that it closes when the delivery pressure drops because excess gas is present in the hydrocarbon.
This type of device comprises the following items downstream from the hydrocarbon storage tank. A pump extracts the hydrocarbon from the storage tank and sends it to a degassing device. The degassing device is generally of the vortex type. Degassed hydrocarbon is taken from the periphery of the degassing device tangentially thereto and is sent towards the valve device. An auxiliary outlet located in the middle of the degassing device recovers hydrocarbon containing gas and returns it to the storage tank.
It turns out that this type of device using a control valve is not always effective in the presence of excess gas. The excess may be due to the fact that when the gas content at the inlet to the degassing device is too high, then the degassing device saturates. In addition, operation of the control valve may be random.
The object of the present invention is to remedy these drawbacks and to provide a system for controlling the valve device which enables the operating reliability of the valve device to be very considerably increased and which also enables the gas content level at which the control valve closes to be adjusted accurately.